Orangish-yellow-emitting Ca3Si2O7:Eu2+ phosphor for application in blue-light based warm-white LEDs

Abstract

A Eu²⁺-activated Ca₃Si₂O₇:Eu²⁺ orangish-yellow-emitting phosphor with strong luminescence was synthesized and its crystal structure was determined on the basis of XRD profiles using synchrotron radiation. The crystal structure was refined by the Rietveld refinement method. The excitation and emission spectra of the Ca₃Si₂O₇:Eu²⁺ phosphor show broad excitation bands in the range of 240–550 nm and a broad yellow emission band centered at 603 nm, depending on the concentration of Eu²⁺. The optimized concentration of Eu²⁺ in the Ca₃Si₂O₇:Eu²⁺ phosphor was determined to be 0.015 mol. The critical distance and average decay time were found to be short and fast, respectively, ranging from 19.74 Å to 13.69 Å and from 2.56 μs to 2.34 μs on increasing the Eu²⁺ doping content. Warm-white light-emitting diodes (LEDs) fabricated using an InGaN-based blue LED chip combined with the Ca₃Si₂O₇:0.015Eu²⁺ phosphor gave color rendering indices between 76.0 and 38.9, correlated color temperatures between 1924 K and 4992 K, and tuned CIE chromaticity coordinates in the range from orangish-yellow (0.543, 0.389) to reddish purple (0.333, 0.219). The color coordinates and emission intensity of a Ca₃Si₂O₇:0.015Eu²⁺-based white LED display were slightly yellow-shifted and the intensity increased on increasing the forward-bias current. These results indicate that orangish-yellow-emitting Ca₃Si₂O₇:0.015Eu²⁺ can serve as a promising candidate for applications in warm-white LEDs.